Astrophysical SE2 factor of the C 12 (α,γ) O 16 reaction through the C 12 (B 11, Li 7) O 16 transfer reaction

The C12(α,γ)O16 reaction plays a key role in the evolution of stars with masses of M>0.55M?. The cross-section of the C12(α,γ)O16 reaction within the Gamow window (Ec.m.=300keV, T9=0.2) is extremely small (about 10-17 barn), which makes the direct measurement in a ground-based laboratory with existing techniques unfeasible. Up until now, the cross-sections at lower energies can only be extrapolated from the data at higher energies. However, two subthreshold resonances, located at Ex=7.117MeV and Ex=6.917MeV, make this extrapolation more complicated. In this work, the 6.917 MeV subthreshold resonance in the C12(α,γ)O16 reaction was investigated via the C12(B11,Li7)O16 reaction. The experiment was performed using the Q3D magnetic spectrograph at the HI-13 tandem accelerator. We measured the angular distribution of the C12(B11,Li7)O16 transfer reaction leading to the 6.917 MeV state. Based on the finite-range distorted wave Born approximation (FRDWBA) and coupled-reaction-channel (CRC) analysis, we derived the asymptotic normalization coefficient (ANC) of the 6.917 MeV level in O16 to be (1.10±0.29) ×1010fm-1, with which the reduced α width was computed to be 18.0±4.7keV at the channel radius of 6.5 fm. Finally, we calculated the astrophysical SE2(300) factor of the ground-state transitions to be 46.2 ± 7.7 keV b. The result for the astrophysical SE2(300) factor confirms the values obtained in various direct and indirect measurements and presents an independent examination of the most important data in nuclear astrophysics.